The present invention discloses a single Tonpilz type piezoelectric transducer which can be used alternately as an emitter for emitting at one or more resonant frequencies and as a wide-band receiver.
1. Field of the Invention
This invention relates to sonar structures.
High power sonar emitter antennas are generally built with an array of Tonpilz type transducers, which comprise a drive consisting of a stack of piezoelectric segments placed between a horn, which is in contact with the water, and a countermass.
In the emission mode, these transducers are excited by an electronic emitter, which emits an oscillating signal of several thousand volts at one or more clearly defined frequencies which are the resonant frequencies of the transducers.
It is advantageous to be able to use the same sonar antennas alternately as emitting and receiving antennas for picking up sound waves, e.g., for detecting the presence of a ship. However, the waves to be received may come in at any sound frequency. If a receiving antenna is to offer acceptable performance, then it must be able to receive sound waves with good sensitivity throughout a broad frequency band covering practically the entire usable band of sound frequencies, i.e., from 1 kHz to 16 kHz.
2. Description of the Prior Art
One solution has been described in a previous patent application (which issued as French Pat. No. 3,570,916, and to which U.S. application Ser. No. 640,145 corresponds), whereby a multifrequency Tonpilz type transducer was obtained for emitting and receiving in several passbands, by placing phase shifting circuits between the piezoelectric segments and the common conductor through which the excitation or output voltage flows, and switching these circuits by means of a logic unit, to the desired passbands.
A main disadvantage of this previous solution was that it calls for complex devices. Also, it allows only several separate passbands to be obtained, separated by frequency bands in which the transducer's sensitivity is poor, and such a transducer does not make it possible to construct receiving antennas covering a very wide band including nearly all the usable sound frequencies, with a good sensitivity.
Furthermore, the known antennas used for emitting and receiving must include switches to isolate the emitter or receiver, alternately.